setting the cms in GIMP using a ruler in the photo

Hi All,

Apologies, I am new to GIMP - I am trying to figure out if there is a way to scale the image in GIMP using a ruler that is in the image. I have taken photos of a number of different fungi in the field and now I need to measure their size. In each photo there is a ruler (that goes both horizontally & vertically) in cm - so basically what I want is a way to tell GIMP that this part of the image is 1cm in size. Is this possible to do?

setting the cms in GIMP using a ruler in the photo

Hi All,

Apologies, I am new to GIMP - I am trying to figure out if there is a
way to scale the image in GIMP using a ruler that is in the image. I
have taken photos of a number of different fungi in the field and now
I need to measure their size. In each photo there is a ruler (that
goes both horizontally & vertically) in cm - so basically what I want
is a way to tell GIMP that this part of the image is 1cm in size. Is
this possible to do?

Then use the Gimp measure tool to show the on canvas size. screenshot 1 measures 10 mm as 74.2 mm Use some guides if they help, the measure tool can snap to intersections.

Then it is a matter of simple proportions to get a scaling factor in my case 74.2 / 10 = 7.42

Open up Image -> Print Size and multiply whatever resolution is there (mine is 180 ppi - comes from the photo) by the scaling factor. Do by hand or Gimp can do simple arithmetic * multiplies / divides.

With that changed the measure tool should now show dimensions corresponding to the image. screenshot 2